1. Field of Invention
The present invention relates to a wafer level sensing package and a manufacturing process thereof, and more particularly to a package and manufacturing process capable of preventing sensing areas from being contaminated during the re-distributing manufacturing process of the sensing wafer and reducing the volume of the package.
2. Related Art
For the current microelectromechanical (MEMS) industry, although the MEMS elements are characterized in miniaturization and integration, the total device cost has remained at a very high level, and thus application of MEMS elements is very limited. Under the impact of individuation and popularization of global communication, it is common to see people each having a cell phone or several phones. Even children just entering school may use cell phones for keeping in contact with their parents. Thus, the consumer group of cell phones greatly expands to encompass children under ten years old, which significantly increases the demands for the phones. Moreover, a research report from Topology in September 2005 pointed out that the number of the global delivered cell phones in 2005 was about 0.760 billion, and the number of the cell phone subscribers would reach 1.685 billion. Meanwhile, it is estimated that the number of the global cell phone subscribers will reach 2.236 billion in 2009. Therefore, the scale of the cell phone market is too large to ignore.
As far as the product properties and design notions of the cell phones, besides basic call function, other functions such as image communication, wireless data communication, network connection, time display, alarm clock, memo, global time-zone, E-mail, personal assistant, GPS navigation, satellite positioning and tracking, e-map, wireless remote control, MP3 music, real-time image, digital photography, digital program reception, horizontal elevation, monitoring alarm, digital game machine, radio, extended memory are also incorporated. Due to the everlasting expansion of functions of a single set, the number of the elements in a cell phone and the probability of device integration may be greatly increased. Unfortunately, in order to meet the consumers' demands for “light, thin, short, small” products, the body volume of a cell phone cannot be enlarged with the expansion of the functions. On the contrary, the whole size of the cell phone is limited within a certain range or even is reduced in accordance with the selling point of “light and chic”. In another aspect, the cell phones have already been plain products in the global market, so the total cost of the cell phones is confined within a reasonable range, and the cell phones cannot be sold at a high price like high-tech equipments or parts. Thus, how to cut down the total cost of the elements employed in a cell phone becomes a challenge in design. Therefore, the mode of mass production at a low cost has become a design criteria and principle for all the elements used in a cell phone, and is also a trend of technical study.
In the cost architecture of the MEMS elements, the packaging cost accounts for 70% to 80% of the total cost of the MEMS elements. Thus, the packaging cost has become the initial essential topic and also the most effective and important way for reducing the cost of the MEMS elements. Moreover, the global wafer level packages still focus on the application of semiconductor packaging, and the structural design considers the problem of the reliability caused by the CTE mismatch between the semiconductor devices and the printed circuit boards in the application of elements in the future. Thus, the wafer level package is designed with an stress release layer and re-arranged wires and pads of a conductive metal layer. Thus, the currently known prior arts mainly focus on the design and format of changing the re-distribution of the wires. Therefore, most of the patents, such as U.S. Pat. No. 6,756,671, U.S. Pat. No. 6,621,164, U.S. Pat. No. 6,790,759, and U.S. Pat. No. 6,350,705, have a common problem that does not disclose the need of forming an opening of the sensing area in the stress release layer. In those wafer level packaging techniques (referring to FIGS. 1A to 1D), a process of adding the re-distributed wires completely on the wafer to form a conductive metal layer between the stress release layer and the original chip pad is adopted. As the stress release layer 11 above the conventional semiconductor wafer 10 covers the entire surface of the wafer 10 except the area of the chip pad 12, the conductive metal layer 14 formed by the patterned photoresist 13 will not contact the chip surface of the wafer 10 during the adding process. However, when this technique is applied to a sensing wafer with an open space, each sensing chip has a sensing area, and the sensing area must keep in contact with the outside during the whole packaging process. That is, as for the sensing wafer, in the wafer level packaging process, the stress release layer must not cover the sensing area of each chip besides the chip pad area. Otherwise, during the subsequent process of adding a conductive metal layer to the wafer, the added metal layer may be formed on the sensing area of each sensing chip of the wafer simultaneously. As such, the material of the sensing layer may be contaminated or the sensing design may be altered, resulting in the failure, decay, deterioration, or non-operation of the sensing function of the sensing layer.